The study provides preliminary support for the ACPI as a promising measure of adolescents’ unfolding coping responses to peer-related stressors in a manner more consistent with predominant conceptualizations of stress and coping. There was evidence for adequate reliability, with the exception of avoidance, as well as overall support for the convergent, divergent, and incremental predictive validity of the ACPI subscales for coping and co-occurring emotional arousal. The authors believe this is the first study to support the presence of intraindividual variability in coping strategy use across the process; that is, adolescents do change in the extent to which they report using various ways of coping as the process unfolds. Such variability in the use of coping strategies accounted for 31-63 percent of the variability in adolescent coping. Although beyond the scope of the current study, examining the timing of or the specific sequencing of coping strategies that may be effective for dealing with certain types of stressors may provide essential information about specific points of intervention in the coping process. In addition, examining unfolding coping patterns may allow moving beyond personality variables regarding how people tend to respond across situations and examine contextual influences such as caregiver coaching or available coping resources that shape and govern the development of coping processes across adolescence. Findings also provide preliminary support for the moderating effect of emotional arousal on coping’s relationship with externalizing symptoms in response to a peer stressor. 4 tables, 2 figures, and 32 references